1. Field of the Invention
This invention relates to improvements in line protectors of the type that are located between equipment to be protected and the outside lines which arrive at the site where the equipment is located.
2. Description of the Prior Art
There are many different protectors which serve to protect equipment from damage as a result of overvoltage and overcurrent conditions on the outside lines entering the site where the equipment is located. One example of such a protector is shown in U.S. Pat. No. 4,168,515 which issued on Sept. 18, 1979 and is assigned to the same assignee as is the present invention (hereinafter "the '515 patent"). The protector shown and described in the '515 patent uses either a gas tube or a carbon element as the means to arrest surges arising from overvoltage conditions on the outside lines.
There has been a trend in the telecommunications industry to use solid state devices as overvoltage arresters in place of either gas tubes or carbon elements. Carbon element and gas tube surge arresting devices rely on an arc discharge to initiate protection. This discharge may cause degradation in the performance of the device which, over time, creates different types of in-service problems. Those problems can range from short circuits to various forms of low voltage operation and current leakage. The degradation can also cause disturbances on the telephone line which are noticeable to the subscriber, who brings them to the attention of the operating company providing the service. The operating company must then have its personnel investigate such "trouble" reports, resulting in the expenditure of both time and money.
Solid state overvoltage arresters, on the other hand, provide noise-free transmission and have a greatly reduced maintenance and longer service life as compared to the carbon element or gas tube surge arresting devices. Therefore, it is desirable to use, wherever possible, solid state overvoltage devices in place of carbon element or gas tube devices. It is further desirable to be able to insert such solid state devices directly in existing line protector units in place of either the carbon element or gas tube surge arresting devices presently used in those units.